1. Field of the Invention
This invention relates generally to organic digesters and more particularly to an improved organic digester apparatus and to an improved method of producing liquid fertilizer and methane gas from organic materials.
2. Description of the Prior Art
The method of manufacturing natural fertilizer and methane gas from organic material by anaerobic digestion is well-known and products sold from this process include a granular fertilizer which is sold under the name Milorganite. The typical method generally includes depositing organic material into a closed container and maintaining the temperature of the organic material at a temperature range of 90.degree. to 105.degree. Fahrenheit for a period of 42 to 60 days.
The typical apparatus has generally included a spherically shaped digester tank and removable roof member. The types of apparatus and methods previously used include the batch type digester in which a quantity of organic material is placed in the digester and retained in the digester until completion of the digesting process, and the displacement type digester in which organic material is continuously, or continually, deposited in the digester, and liquid fertilizer is continously, or continually, removed from the digester.
The problem which is inherent with the batch type digester is that organic material can be deposited in the digester only after completion of the digesting cycle and the removal of completed fertilizer from the digester. The problem which is inherent with the displacement type digester is that incompletely digested material is mixed with the completely digested organic material which has been transformed into liquid fertilizer; so that, when the liquid fertilizer is removed from the displacement type digester, rather than being pure fertilizer, it is contaminated with incompletely digested organic material.